1. Field of the Invention
The present invention relates to a semiconductor device having a conductive film connected to a pad on a semiconductor substrate and a production process thereof.
2. Description of Related Art
In a chip-on-chip structure in which active surfaces of a pair of semiconductor chips are overlapped with each other, and in a flip chip bonding structure in which a semiconductor chip is joined to a wiring board with its active surface opposed to the wiring board, a projection for electrical connection called a bump is provided on the active surface of the semiconductor chip. FIG. 3 illustrates construction in the vicinity of a surface of the semiconductor chip.
A pad 52 to which a part of an external wiring is exposed is provided on an active surface 51a of a semiconductor substrate 51. The active surface 51a of the semiconductor substrate 51 is covered with a polyimide film 54 having an opening 53 to which the pad 52 is exposed. A bump 55 is arranged on the pad 52 in the opening 53. The bump 55 projects from a surface of the polyimide film 54.
The bump 55 is formed by electroless plating, for example. In the electroless plating, a metal film having good adhesive properties cannot be formed on the surface of the polyimide film 54. By merely growing a thick film of a conductor such as gold or copper on the pad 52 inside the opening 53, therefore, the bump 55 is formed.
However, it takes long to form the thick film by the electroless plating. Accordingly, it takes significantly long to fill in the opening 53 formed in the polyimide film 54 and form the bump 55 projecting from the surface of the polyimide film 54. Therefore, time required to produce the semiconductor chip is long.
An object of the present invention is to provide a semiconductor device, having a connecting member, whose productivity can be improved and a production process thereof.
Another object of the present invention is to provide a process of producing a semiconductor device, in which a low-resistive conductive film having good adhesive properties can be formed on a surface of an insulating film on a semiconductor substrate in a short time.
A semiconductor device according to the present invention comprises a pad for electrical connection provided on a semiconductor substrate; a first insulating film with which a surface of the semiconductor substrate is coated and having an opening to which the pad is exposed; a conductive film joined to the pad on a bottom surface of the opening of the first insulating film and extending to a surface of the first insulating film outside the opening; a second insulating film with which the conductive film is coated and having an opening to which a part of the conductive film is exposed; and a connecting member arranged so as to be joined to the conductive film inside the opening of the second insulating film.
The semiconductor device can be produced by a production process comprising the steps of coating a surface of a semiconductor substrate, provided with a pad for electrical connection, with a first insulating film having an opening to which the pad is exposed; modifying a surface of the first insulating film and an inner wall surface of the opening; forming by an ion-exchange reaction a thin conductive film with which the surface of the first insulating film, the inner wall surface of the opening, and a surface of the pad exposed on a bottom surface of the opening is coated; thickening the thin conductive film by electroplating with power being fed using the thin conductive film; forming a second insulating film with which the thickened conductive film is coated and having an opening to which a part of the conductive film is exposed; and forming a connecting member joined to the thickened conductive film inside the opening of the second insulating film.
According to the process, by modifying the surface of the first insulating film and the inner wall surface of the opening formed in the first insulating film, the thin conductive film having good adhesive properties can be formed by utilizing the ion-exchange reaction on the modified surfaces. Power can be fed using the thin conductive film, thereby making it possible to thicken the thin conductive film by the electroplating. The conductive film can be thickened in a short time by the electroplating. As a result, the thickened conductive film having good adhesive properties can be quickly formed on the first insulating film. After the thickened conductive film is then coated with the second insulating film, and the opening is formed in the second insulting film, the connecting member joined to the thickened conductive film may be formed in the opening.
The surface modification processing for the first insulating film may be processing for introducing a cation exchange group into the surface of the first insulating film. The surface of the first insulating film which has been subjected to the surface modification processing is brought into contact with a solution containing ions of a metal material to compose the conductive film, thereby making it possible to produce the ion-exchange reaction. By the ion-exchange reaction, the metal ions are replaced with the cation exchange group, and the cation exchange group is sucked by the surface of the first insulating film.
The connecting member may be a bump for connection to another solid device (e.g., another semiconductor chip or wiring board).
The connecting member may be another conductive film joined to the conductive film on the bottom surface of the opening in the second insulating film and extending to the surface of the second insulating film. In this case, a so-called multi-layered wiring structure is constituted by a two-layer conductive film insulated by the second insulating film.
The first insulating film may be composed of polyimide resin. In this case, the modification processing for the surface of the first insulating film and the inner wall surface of the opening formed in the first insulating film may be processing for cleaving an imide ring of the polyimide resin using a potassium hydroxide solution, for example, and introducing a carboxyl group serving as the cation exchange group into the surface of the first insulating film. Thereafter, the first insulating film is immersed in the solution containing the ions of the metal material composing the connecting member, thereby making it possible to produce the ion-exchange reaction on the surface of the first insulating film and form the connecting member composed of the metal material on the surface of the first insulating film, the inner wall surface of the opening, and the surface of the pad.
As a material for the first insulating film, epoxy resin, for example, can be used in addition to the polyimide resin. In this case, the surface modification processing for the first insulating film maybe processing for immersing the first insulating film in a sulfuric acid solution to introduce a sulfo group serving as the cation exchange group into its surface. When an epoxy resin film which has been thus subjected to the surface modification processing is immersed in the solution containing the metal ions to produce the ion-exchange reaction, the metal ions are sucked by the surface of the first insulating film.
As a material for the first insulating film, resin including an imide bond or an acido bond or including both an imide bond and an acido bond can be used in addition thereto.
As the second insulating film, the resin including an imide bond or an acido bond or both an imide bond and an acido bond can be used, in addition to the polyimide resin or the epoxy resin, as a material composing the second insulating film, similarly to the first insulating film. Particularly when a multi-layered wiring structure is formed using a pair of conductive films insulated by the second insulating film, it is preferable that the surface of the second insulating film and the inner wall surface of the opening are subjected to the above-mentioned surface modification processing using the polyimide resin or the epoxy resin as the material composing the second insulating film.
A process according to another mode of the present invention comprises the steps of forming an insulating film on a semiconductor substrate; modifying a surface of the insulating film; forming a thin conductive film by an ion-exchange reaction on the modified surface of the insulating film; and thickening the thin conductive film by electroplating for feeding power using the thin conductive film.
According to the process, the conductive film having good adhesive properties can be formed on the surface of the insulating film by performing the ion-exchange reaction subsequently to the surface modification processing for the insulating film. The thin conductive film is thickened by the electroplating, thereby making it possible to form a low-resistive conductive film having good adhesive properties in a short time on the insulating film. This can contribute to an improvement in the productivity of the semiconductor device.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.